U.S. patent number 4,670,410 [Application Number 06/717,276] was granted by the patent office on 1987-06-02 for method for reducing attrition of particulate matter in a chemical conversion process.
This patent grant is currently assigned to Atlantic Richfield Company. Invention is credited to Lloyd A. Baillie.
United States Patent |
4,670,410 |
Baillie |
June 2, 1987 |
Method for reducing attrition of particulate matter in a chemical
conversion process
Abstract
A method for restoring the catalytic activity of solid particles
using an improved apparatus for separating solid particles from
vapor is disclosed. The apparatus includes a novel inlet system, a
novel particle outlet system and a chamber having novel dimensional
relationships which result in an apparatus that separates solid
particles from vapor with less attrition, or "break-up" of
particulate matter, while maintaining a high separation efficiency
at high loading conditions, e.g., the apparatus maintains a
tangential wall velocity of less than about 50 feet per second and
separates, from a mixture of solid particles and vapor, more than
about 95% of the solid particles that are larger than about 20
microns in diameter while processing more than about 200 cubic feet
of the mixture per second. This apparatus is particularly suited to
at least partially separating solid particles from a mixture of
vapors and solid particles, the mixture being of the type which
arises when restoring the catalytic activity of solid particles
previously used to promote or carry out a chemical conversion such
as hydrocarbon cracking.
Inventors: |
Baillie; Lloyd A. (Homewood,
IL) |
Assignee: |
Atlantic Richfield Company (Los
Angeles, CA)
|
Family
ID: |
26957477 |
Appl.
No.: |
06/717,276 |
Filed: |
March 28, 1985 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
275562 |
Jun 22, 1981 |
|
|
|
|
Current U.S.
Class: |
502/41; 208/161;
208/164; 422/144; 502/34; 55/459.1; 95/271 |
Current CPC
Class: |
B01J
8/0055 (20130101); B01J 38/30 (20130101); C10G
11/18 (20130101); B04C 5/04 (20130101); B04C
5/081 (20130101); B01J 38/38 (20130101) |
Current International
Class: |
B01J
8/00 (20060101); B01J 38/38 (20060101); B01J
38/30 (20060101); B01J 38/00 (20060101); C10G
11/00 (20060101); C10G 11/18 (20060101); B01J
038/20 (); B01J 008/24 (); C10G 011/05 (); B01D
045/12 () |
Field of
Search: |
;502/21,41-44,34
;208/161-164 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"A Graphical Method of Sizing Cyclone Dust Collectors" L. Monroe;
Heating & Ventilating--Dec. 1950, pp. 63-66. .
"Cyclone Eficiency Studies"--A. Rushton et al. Filtration &
Separation Mar./Apr. 1978--pp. 159-162..
|
Primary Examiner: Konopka; P. E.
Attorney, Agent or Firm: Traut; Donald L. Martin; Michael
E.
Parent Case Text
This application is a continuation of co-pending application Ser.
No. 275,562, filed June 22, 1981, now abandoned.
Claims
What is claimed is:
1. A method for restoring the catalytic activity of solid particles
previously used to promote hydrocarbon conversion, with
deactivating carbonaceous deposit material thereon, the major
portion by weight of said particles having diameters in the range
from about 10 microns to about 500 microns, wherein in a
regeneration zone said particles are contacted with
oxygen-containing vapor at conditions to form a first fluid stream
comprising a mixture of particles and vapor, said method including
the steps of:
providing an apparatus having a body which includes a chamber
defined in part by a generally cylindrical wall, fluid stream inlet
means opening into said chamber for introducing said first fluid
stream into said chamber, fluid outlet means in communication with
said chamber for withdrawing a second fluid stream substantially
free of said particles, and particle outlet means for withdrawing
particles separated from said first fluid stream;
introducing said first fluid stream into said chamber in a
plurality of separate fluid inlet streams along a plurality of
separate paths substantially tangentially into said chamber and in
such a way that the paths of said plurality of fluid inlet streams
will impinge on a portion of the path of a fluid inlet stream
downstream in the direction of flow of said fluid inlet streams to
induce said particles in the impinging streams to be deflected away
from said wall to reduce contact of said particles with said wall
to maintain a high degree of separation efficiency while decreasing
particle attrition;
withdrawing said second fluid stream through said fluid outlet
means; and
withdrawing particles separated from said first fluid stream
through said particle outlet means.
2. The method set forth in claim 1 wherein:
said first fluid inlet stream is provided at a flow rate of at
least about 200 cubic feet per second and the step of providing
said apparatus includes the step of determining the radius "R.sub.w
" of said chamber with respect to a central axis of said chamber,
the height "h" of said chamber, the inlet area "A.sub.i " of said
fluid stream inlet means, and the radius "R.sub.i " of said fluid
stream inlet means with respect to said central axis such that;
(1) R.sub.i h/R.sub.w 0.89 is less than about 11 ft.sup.1.1 ;
(2) R.sub.i A.sub.i is greater than about 16 ft.sup.3 ; and
(3) hA.sub.i is greater than about 56 ft.sup.3.
3. The method set forth in claim 2 wherein:
the step of determining R.sub.w includes selecting R.sub.w to be
between about 4 feet and 10 feet.
4. The method set forth in claim 2 wherein:
the step of determining "h" includes selecting "h" to be between
about 4 feet and 50 feet.
5. The method set forth in claim 1 wherein:
said first fluid inlet stream is provided at a flow rate of at
least about 200 cubic feet per second, wherein said particles have
a density "d" and said first fluid stream has a viscosity "n", and
the step of providing said apparatus includes the step of
determining with respect to the central axis of said chamber, the
radius "R.sub.w " of said chamber, the radius "R.sub.i " of said
fluid stream inlet means, the height "h" of said chamber, the inlet
area "A.sub.i " of said fluid stream inlet means, the outlet area
"A.sub.o " of said outlet means, the radius "R.sub.o " of said
outlet means such that; ##EQU4## where D is the critical particle
size in the range of about 8 microns to about 12 microns, F is the
fluid stream flow rate in the cubic feet per second, V.sub.w is the
fluid tangential velocity at the chamber wall and is less than
about 50 feet per second, and K.sub.i, K.sub.a, K.sub.h and K.sub.o
are constants having values, respectively, of about 3.8, 0.016,
14.0 and 0.017.
6. A method for restoring the catalytic activity of solid particles
previously used to promote hydrocarbon conversion wherein in a
regeneration zone said solid particles are contacted with vapor at
conditions to form a first fluid stream comprising a mixture of
solid particles and vapor, said method including the steps of:
providing an apparatus having a body which includes a chamber
defined in part by a generally cylindrical wall, fluid stream inlet
means opening into said chamber for introducing said first fluid
stream into said chamber, fluid outlet means in communication with
said chamber for withdrawing a second fluid stream substantially
free of said solid particles, and particle outlet means for
withdrawing solid particles separated from said first fluid
stream;
introducing said first fluid stream into said chamber in a
plurality of separate fluid inlet fluid streams along a plurality
of separate paths in such a way that the paths of each of said
plurality of fluid inlet streams will impinge on a portion of the
path of at least one other of said fluid inlet streams in the
direction of flow of said fluid inlet streams to induce said solid
particles in the impinging streams to be deflected away from said
wall to reduce contact off said solid particles with said wall to
maintain a high degree of separation efficiency while decreasing
particle attrition;
withdrawing said second fluid stream through said fluid outlet
means; and
withdrawing solid particles separated from said first fluid stream
through said particle outlet means.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved apparatus and method for
restoring catalytic activity of solid particles previously used to
promote chemical conversion processes. More particularly, the
invention relates to a method and apparatus for separating, at high
temperatures, solid particulate matter, used in promoting
hydrocarbon conversions, from a mixture of vapor and solid
particulate matter. The invention provides a technique for
maintaining both high separation efficiency and low particulate
attrition at high loading conditions.
In many instances throughout the chemical and hydrocarbon
processing industries, chemical reactions occur which are promoted
by relatively small catalyst particles in fluidized bed catalytic
reactions (e.g., catalyst diameters ranging from about 10 microns
to about 500 microns.) One process used extensively in the
petroleum industry which utilizes small catalyst particles is the
catalytic cracking of higher boiling hydrocarbons to gasoline and
other lower boiling components. The apparatus used for carrying out
this chemical conversion (e.g., cracking of a feedstock) or
reforming (e.g., hydrocarbon gas oil) includes a reaction zone
where the relatively small catalyst particles and feedstock are
contacted at chemical conversion (e.g., hydrocarbon cracking or
reforming etc.) conditions to form at least one chemical conversion
product (e.g., hydrocarbons having a lower boiling point than the
hydrocarbon feedstock and/or a higher octane rating.)
Often, while promoting the desired chemical conversion, the
catalyst particles have deposited thereon carbonaceous materials
such as carbon, coke and the like which act to reduce the catalytic
activity of these particles. Apparatus which is used to restore the
catalytic activity of such particles often includes a regeneration
zone where the deposit-containing solid particles are contacted
with oxygen-containing vapor at conditions to combust at least a
portion of such deposited material.
Operation of each of the systems referred to above involves the
formation of a mixture of solid particles and vapor followed at
some point in time with a separation of at least a portion of the
solid particles from the vapor-particle mixture. Therefore, both
the apparatus for carrying out chemical conversion and the
apparatus for restoring the catalytic activity of the solid
catalyst particles include at least one separation apparatus
wherein the mixture of solid particles and vapor formed in either a
reaction of a regeneration zone, respectively, is at least
partially separated. Such separation apparatus often involves a
conventional cyclone precipitator or separator.
Processing solid catalyst particles through cyclone precipitators
may cause the solid catalyst particles to break up and/or form
"fines" by attrition. The resulting particle fines are often of
such a size that they cannot be effectively separated from the
vapor, and are lost from the system. This results in the loss of
valuable catalyst and the discharge of potential air pollutants.
Accordingly, it is advantageous to provide for a cyclone having low
or reduced rates of attrition of the solid catalyst particles.
"Attrition" generally refers to the fraction of solid particles
which are converted to less than about 20 microns.sup.1/ in average
diameter as a result of one or more collisions between solid
particles, alone or in connection with a solid cyclone wall or
other surface. A cyclone with "low attrition" is one in which less
than about 3.0.times.10.sup.-6 of all catalyst particles are
converted to less than about 20 micron size during a separation of
particles from vapor therein.
In addition to low attrition, cyclones preferably have a high
separation efficiency, e.g., an efficiency in separating from the
mixture of solid particles and vapor about 95-99% of the solid
particles larger than about 20 microns in diameter. However,
conventional cyclone separation art teaches that in scaling a
cyclone for high loading conditions (e.g., processing a stream
having a high volumetric flow rate "F", typically on the order of
about 200-600 cubic feet of fluid per second) either high
separation efficiency or low attrition must be sacrificed.
Engineers faced with the problem of specifying the dimensions of a
cyclone for high loading conditions try for optimum balance in the
trade-off between separation efficiency and attrition.
In order to attain both high separation efficiency and low
attrition, the prior art has required that smaller sized cyclones
should be used. The rationale for this position is based upon a
relatively complex relationship between the flow patterns inside
the cyclone, the tangential velocity of the particle at the cyclone
wall and the effect of collisions between the cyclone wall and the
solid particles. For example, in order to provide high separation
efficiency, the gas revolution velocity (and thus the motion of the
solid particles toward the outer walls) should be high. However,
high centrifugal forces create strong friction forces between the
solid particles and the cyclone wall, and these strong friction
forces coupled with high tangential velocities at the cyclone wall
increase the rate of attrition. In order to provide low attrition,
the tangential wall velocity should be low. However, lower
tangential velocities in conventional cyclones designed for high
loading conditions are typically achieved by reducing the velocity
of gas revolutions, which, in turn, reduces separation efficiency.
Thus arises the trade-off between separation efficiency and
attrition. The use of smaller sized cyclones minimizes the
disadvantageous trade-off because smaller radius cyclones provide
greater centrifugal forces at relatively slower tangential
velocities.
The use of smaller sized cyclones leads to further complications,
particularly in the high volume applications which characterize
many industries and the petroleum industry in particular. For
example, the smaller sized cyclones have a smaller operating
capacity. In order to process a product stream of a given size, two
or more smaller sized cyclones must be used in the place of one
larger sized cyclone. The smaller sized cyclones in such situation
are typically set up in parallel operation with the product stream
divided between them, resulting in a more complex and more
expensive design. Importantly, the use of multiple, smaller
cyclones results in a more space consuming design than a single
larger cyclone.
In some situations, the option of using several smaller size
cyclones may not be available as a practical matter because the
necessary amount of space does not exist. Inadequate space is
especially likely to present a problem where new cyclones are being
installed to upgrade an existing facility; the available space in
the old facility may not adequately accommodate several, smaller
new cyclones. Frequently, even in new chemical processing plants,
the amount of space provided for restoration of the catalytic
particles is inadequate to effectively allow using the smaller
sized units, assuming that such a choice were otherwise
practicable.
Heretofore, no adequate alternative choice for providing a high
capacity, high efficiency, low attrition cyclone or restoration
method, particularly one operable within commonly available space
limitations, has been available. The present invention provides a
solution to this problem.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an apparatus and
method for carrying out chemical conversions (e.g., cracking or
reforming) of a feedstock (e.g., hydrocarbon) using solid catalyst
particles to promote the conversion, which provides both high
separation efficiency and low particle attrition at high loading
conditions.
Another object of the present invention is to provide an improved
apparatus and method for restoring the catalytic activity (e.g.,
for hydrocarbon cracking or reforming) of solid catalyst particles,
which provides both high separation efficiency and low particle
attrition at high loading conditions and high temperatures.
Still another object of the present invention is to provide an
improved method and apparatus for separating particulate matter
from vapor which provides both high separation efficiency and low
attrition at high loading conditions.
A further object of the present invention is to provide a method
and apparatus which accomplishes separation of solid catalyst
particles from vapor with relatively reduced space
requirements.
Yet another object of the present invention is to provide an
improved fluid inlet to a cyclone which provides reduced
particulate attrition during the introduction of a particulate
matter/vapor mixture into the cyclone chamber at high velocity.
Yet still a further object of the present invention is to provide a
vortex reflecting and centering device for preventing the
re-entrainment of particulate matter that has been effectively
separated from a particulate matter/vapor mixture in a cyclone and
for adjusting the location of a vortex in a cyclone.
Other objects of this invention are clear to one of skill in the
art based upon the teachings of this specification.
In one embodiment, the present invention involves an improved
apparatus for carrying out a chemical conversion of a feedstock.
This apparatus includes a chemical reaction zone wherein the
feedstock (e.g., a substantially hydrocarbon material) is contacted
with solid particles capable of promoting chemical conversion
(e.g., hydrocarbon cracking) at chemical conversion conditions to
form at least one chemical conversion product and a mixture of
solid particles and vapor. The major portion of the solid
particles, preferably at least about 90% by weight thereof, has a
diameter in the range from about 10 microns to about 500 microns,
preferably from about 20 microns to about 200 microns. At least one
separation device in fluid communication with the reaction zone is
provided to at least partially separate the mixture of solid
particles and vapor. The separation device comprises a chamber
defined by an interior surface which can be of a variety of shapes,
cylindrical being preferred, and an inlet to introduce a fluid
stream mixture of solid particles and vapor into the chamber in
fluid communication between the reaction zone and the chamber. The
inlet is situated so that movement of the fluid stream mixture
within the chamber causes the solid particles to preferentially
move, in vortex fashion, toward the interior surface. The
separation device also includes an outlet for particles from the
chamber which allows at least a portion of the solid particles that
have been effectively separated from the vapor and collected along
the interior surface to exit from the chamber; and a fluid outlet
from the chamber, which allows at least a portion of the separated
vapor component of the mixture to exit from the chamber.
The separation device of the present invention involves a chamber,
an inlet and fluid outlet characterized by novel dimensions and
dimensional relationships to provide low attrition and high
separation efficiency, particularly at high loading conditions.
These unique dimensions and dimensional relationships are defined
in detail later.
An improved method of chemical conversion (e.g., hydrocarbon
cracking or reforming) utilizing such improved apparatus has also
been developed.
In an additional embodiment, the present invention involves an
apparatus for restoring the catalytic activity of solid particles
which have previously been used to promote chemical conversion
(e.g., hydrocarbon cracking) and have deactivating carbonaceous
material deposited thereon, the major portion, preferably at least
about 90% by weight of the solid particles having diameters in the
range from about 10 microns to about 500 microns, preferably from
about 20 microns to about 200 microns. This apparatus includes a
regeneration zone wherein solid particles having deactivating
deposits thereon are contacted with oxygen-containing vapor under
conditions sufficient to combust at least a portion of the deposits
and to form a mixture of solid particles and vapor having a high
volumetric flow rate. The regeneration zone is in fluid
communication with at least one separation device wherein at least
a portion of the solid particles are separated from the mixture.
The separation device comprises a chamber defined by an interior
surface and an inlet to allow entry of the fluid stream mixture
from the regeneration zone into the chamber. The inlet is situated
so that movement of the fluid stream mixture within the chamber
causes solid particles to preferentially move in vortex fashion
toward the interior surface. The separation device also has (1) a
particle outlet to allow at least a portion of the solid particles
of the mixture that have effectively separated from the vapor and
collected along the interior surface to exit from the chamber and
(2) a fluid outlet from the chamber to allow at least a portion of
the separated vapor component of the mixture to exit from the
chamber. The separation device of this embodiment also includes the
novel dimensions and dimensional relationships which, as previously
mentioned, will be defined later.
An improved method for restoring the catalytic activity of solid
particles utilizing this improved apparatus has also been
developed.
The apparatus of the present invention includes at least one
separation device. However, the apparatus often involves staged
separators, e.g., two or more separators in series. The second and
following separators, if any, are in fluid communication with the
first or previous separators, if any, and receive a fluid product
therefrom for further processing. However, the present improved
separator can advantageously be used as either the first and/or
succeeding separator in such a series.
The reaction zone and the regeneration zone can each have a volume
as great as about 100,000 cubic feet or more, preferably from about
20,000 cubic feet to about 50,000 cubic feet. Different sized
reactions zones and regeneration zones produce different amounts of
particulate matter/vapor mixture, and the separation devices of
this invention should be sized according to the volume of product
generated by the preceding unit.
The separation device of the present invention is designed to
separate particulate matter from a fluid stream mixture of vapor
and particulate matter at high loading conditions, e.g., the stream
has a high volumetric flow rate "F" of at least 200 cubic feet per
second, preferably not in excess of about 600 cubic feet per second
and still more preferably between about 200 and about 600 cubic
feet per second. As mentioned, the separation device includes a
body, a fluid inlet, a fluid outlet and a particle outlet.
The body of the separation device defines a chamber of radius
"R.sub.w " and height "h". In preferred form, the body includes an
upright cylindrical wall portion, a bottom portion and a top
portion. The chamber also includes a central axis, a radius
"R.sub.w " equal to the distance between the central axis and the
cylindrical wall portion, and a height "h" equal to the average
distance between the fluid outlet and the bottom portion along a
line substantially parallel to the central axis.
The fluid inlet permits the introduction of the first fluid stream
into the chamber. The inlet is secured to the body and includes an
inlet area "A.sub.i " and an inlet radius "R.sub.i ". In one
embodiment, the inlet includes a conduit in fluid communication
with the source of vapor and particulate matter mixture, preferably
the reaction zone or the regeneration zone, and with the chamber.
The conduit defines an inlet opening having a predetermined
cross-sectional area. Although the inlet conduit may discharge into
the chamber from any convenient angle, the inlet conduit preferably
empties either substantially parallel to the central axis of the
chamber (e.g., a top inlet to a chamber positioned so that the
central axis of the conduit is substantially vertical) or
substantially tangential to the interior surface of the chamber. In
a preferred embodiment, the inlet area "A.sub.i " equals the
cross-sectional area of the inlet opening, and the inlet radius
"R.sub.i " equals the average distance between the inlet opening
and the central axis.
The fluid outlet permits the withdrawl of a second fluid stream
from the chamber. The fluid outlet is secured to the body of the
separation device and includes a fluid outlet area "A.sub.o " and a
fluid outlet radius "R.sub.o ". In one embodiment the fluid outlet
includes a conduit in fluid communication with the chamber and
either a second separation device or a further processing unit,
thereby defining a fluid outlet opening. The conduit preferably
extends from the chamber substantially parallel to and concentric
with the central axis of the chamber. In a preferred embodiment,
the fluid outlet area "A.sub.o ", equals the cross-sectional area
of the conduit at the outlet opening, and the fluid outlet radius
"R.sub.o " equals the average distance between the fluid outlet
opening and the central axis.
The particle outlet permits the withdrawl of particulate matter
from the chamber. The particle outlet is secured to the body and
communicates with the chamber.
The separation device of the present invention is characterized by
satisfying all of the following conditions:
(1) R.sub.i h/R.sub.w.sup.0.89 is less than about 11 ft.sup.1.1 ;
and preferably less than about 9 ft.sup.1.1 ;
(2) R.sub.i A.sub.i is greater than about 16 ft.sup.3 ; and
preferably greater than about 19 ft.sup.3 ; and
(3) hA.sub.i is greater than about 56 ft.sup.3 ; and preferably
greater than about 67 ft.sup.3.
A separation device having the indicated dimensional relationships
provides low attrition, high separation efficiency of particulate
matter and high space efficiency at high loading conditions.
As noted, the sepration device of the present invention is
preferably directed to applications involving high loading
conditions, e.g. conditions that involve a volumetric flow rate "F"
of between about 200 and about 600 cubic feet per second.
Conventional cyclones intended for comparable flow rates having
high loading conditions can be characterized by a chamber radius
"R.sub.w ", which is less than about 3 feet. The previously defined
relationships for the separation device of the present invention
are significantly different than the ratios for conventional
cyclones intended for comparable high loading conditions.
In addition to its unique dimensional ratios, the separation device
of the present invention is also characterized by its unique
ability to provide a low rate of attrition and a high rate of
separation efficiency at high loading conditions. The invention
provides novel relationships for determining the dimensions of
certain elements (e.g., "R.sub.w ", "h", "A.sub.i ", "R.sub.i " and
"R.sub.o ") in relation to the operating parameters for the device.
In order to more fully understand these relationships, it is
necessary to first discuss the techniques used to determine low
attrition and high separation efficiency.
As previously mentioned, low attrition is conventionally defined in
relation to a separation operation wherein less than about
3.0.times.10.sup.-6 fraction of solid particles which collide with
the cyclone interior surface are converted to fines of less than
about 20 micron size. A more practical definition of low attrition
has been developed in connection with the present invention,
namely, that low attrition for catalyst particles used to promote
hydrocarbon conversion exists if the separation of the catalyst
particles involves a tangential wall velocity "V.sub.w ", within
the cyclone less than about 50 feet per second, preferably less
than about 40 feet per second. It has been found in connection with
this invention that the maintenance of such tangential wall
velocities in the cyclone provides acceptable low attrition when
dealing with catalyst particles used to promote hydrocarbon
conversion.
Similarly, high separation efficiency for first stage cyclones may
be defined in relation to the capability of separating from a
mixture of solid particles and vapor about 95-99% of the solid
particles having a mean particle size greater than about 20
microns. However, a more practical definition of high separation
efficiency has been developed in connection with the present
invention. For purposes herein, high separation efficiency is
characterized by a separation device which operates with a critical
particle diameter "D", of less than about 12 microns, preferably
between 8 and about 12 microns and most preferably between about 9
and 11 microns. In order to understand and define the concept of
"critical particle diameter", it is necessary to review the
operation of a cyclone in somewhat greater detail.
The fluid inlet introduces the fluid mixture into the cyclone and,
in combination with the cyclone wall and fluid outlet, transforms
linear flow into helical or vortex flow. Once the fluid mixture
leaves the inlet, a vortex is established within the cyclone having
an axial component in the direction of the particle outlet, and a
tangential component perpendicular to the chambers' radius "R.sub.w
".
The cyclone separates particles from vapor by means of the
centrifugal force which is exerted on the solid particles by the
circular pattern of vortex flow. This force tends to drive the
particles to the wall of the cyclone body where they are no longer
entrained in the mixture and collect with other particles. The
magnitude of the centrifugal force depends upon the nature of the
vortex flow in different sections of the cyclone. Counteracting
forces, caused by the radially inward flow of vapor exiting the
fluid outlet, tend to offset the separating centrifugal forces. The
particles at the wall move toward the particle outlet by virtue of
the axial component of the vortex flow, aided, if the axis is
vertical, by gravity.
However, solid particles within the core of the vortex and
particularly those near the fluid outlet are more greatly effected
by the counteracting forces of the inward radial gas flow, and such
particles tend to be entrained in the fluid outlet stream. The
magnitude of these counteracting forces are primarily related to
the shape and surface area of the solid particles and the viscosity
and velocity of the inward radial gas flow. Critical particle
diameter refers to a solid particle, assumed to be of spherical
shape, having a size such that the particle has a 50-50 chance of
being entrained in the fluid outlet stream when the particle is at
a point immediately adjacent the fluid outlet. It has been found in
connection with this invention that suitably high separation
efficiency of catalyst particles used to promote hydrocarbon
conversion is provided by a separation means that operates with a
critical particle diameter "D" of between about 8 and about 12
microns.
The critical features of the present separation device, the chamber
radius "R.sub.w ", chamber height "h", inlet area "A.sub.i ", inlet
radius "R.sub.i ", and outlet radius "R.sub.o " are calculated from
the operating parameters, volumetric flow rate "F", tangential wall
velocity "V.sub.w ", and critical particle size "D" according to
the following equations: ##EQU1## where: K.sub.i =about 3.8
K.sub.a =about 0.016
K.sub.h =about 14
K.sub.o =about 0.017
and where "d" and "n" are constants equal to the density of the
particulate matter and the viscosity of the particulate
matter/vapor mixture, respectively. The critical particle size "D",
can be calculated as follows: ##EQU2##
More specifically, according to the present invention the
separation means includes a chamber radius "R.sub.w ", of between
about 4 feet to about 10 feet or more, preferably from about 4 feet
to about 6 feet, and a height "h", ranging from about 4 feet to
about 50 feet or more, preferably from about 5 feet to about 20
feet, and most preferably from about 5 feet to about 12 feet. The
separation apparatus further includes an inlet area "A.sub.i ", of
between about 4 feet.sup.2 and about 12 feet.sup.2, an inlet radius
"R.sub.i ", of between about 2.5 feet and about 7 feet, and an
outlet radius "R.sub.o ", of between about 0.5 and about 2
feet.
A separation device designed according to the present invention for
a particular application has specific dimensions calculated
generally according to Relationships 4-8. Although the prior art
may include a cyclone having certain features with certain
dimensions that may fall within these relationships, the present
invention, in contrast to the prior art, requires that all of the
dimensions fall within the ranges of these equations.
In addition to the advantageous operating parameters previously
described, another advantage of determining the dimensions of the
separator means according to Relationships 4-8 is that the
separation device operates substantially independently of
temperature. That is, the separation device of this invention
provides consistent separation over a wide range of operating
temperatures. This advantage is in contrast to known prior art
which teach that the size of a separation device should be adjusted
for significant operating temperature changes. See, Alexander, R.
M. Proc. Austral. Inst. Min. Met., (N.S.), Vol. 152 (1949).
In another embodiment, the present invention comprises an improved
inlet which introduces the particulate matter/vapor mixture into
the chamber at a high velocity and in a predetermined direction
while minimizing contact of the solid particles with any solid
surface, thereby increasing contrifugal forces and separation
efficiency while minimizing attrition attributable to the inlet
flow. The inlet comprises a plurality of inlet vanes which divide
the inlet fluid mixture into a plurality of high velocity inlet
streams, at least one inlet stream being associated with each vane.
The inlet vanes are preferably positioned symmetrically about the
body. The inlet stream associated with each inlet vane deflects
other inlet streams associated with adjacent inlet vanes to induce
particles contained therein to move away from any solid surface,
for example, the body of the chamber wall or any adjacent inlet
vanes. For example, the inlet stream associated with a first inlet
vane is deflected away from any solid surface by an inlet stream
associated with a second adjacent inlet vane, and the second by a
third adjacent inlet and so on. In this manner, each inlet
minimizes contact of the particulate matter with the body wall or
other solid objects and thus facilitates high centrifugal force and
high separation efficiency while minimizing or reducing particle
attrition.
Preferably, there are at best, three suitably arranged inlet vanes
in order to minimize contact of solid particles with solid
surfaces, and more preferably at least about 4, and still more
preferably at least about 5. Generally, anywhere from about 5 to
about 12 suitably arranged inlet vanes are useful in this
invention.
In still another aspect, the separation device of the invention
comprises a vortex reflector which includes a plate member,
connected to the body, that divides the chamber into a separation
zone and a collection zone and a reflecting disk mounted within the
separation zone of the chamber directly between the plate member
and the fluid outlet. The vortex reflector prevents particulate
matter that has been separated from the mixture from being
re-entrained along the bottom of the cyclone chamber and into the
fluid oulet stream. The reflecting disk preferably has an area
which is at least substantially equal to the area of the outlet
means.
Although the present invention is useful in many chemical
conversions and catalyst regenerations, the apparatus and methods
of this invention find particular applicability in systems for the
catalytic cracking of hydrocarbons and the regeneration of
catalysts so employed. Such catalytic hydrocarbon cracking often
involves converting (i.e., cracking) heavier or higher boiling
hydrocarbons to gasoline and other lower boiling components, such
as hexane, hexene, pentane, pentene, butane, butylene, propane,
propylene, ethane, ethylene, methane and mixtures thereof. The
substantially hydrocarbon feedstocks typically comprises a gas oil
fraction, e.g., derived from petroleum, shale oil, tar sand oil,
coal and the like. Such feedstock may comprise a mixture of
straight run, e.g. virgin, gas oil. Such gas oil fractions often
boil primarily in the range from about 400.degree. F. to about
1000.degree. F. Other substantially hydrocarbon feedstocks (e.g.,
other high boiling or heavy fractions of petroleum, shale oil, tar
sand oil, coal and the like) can be cracked using the apparatus and
method of the present invention. Such substantially hydrocarbon
feedstocks often contain minor amounts of contaminants, e.g.,
sulfur, nitrogen and the like.
Hydrocarbon cracking conditions are well known and often include
temperatures from about 850.degree. F. to about 1100.degree. F.,
conditions usually include pressures of up to about 100 psig.;
catalyst to oil ratios of from about 5 to 1 to about 25 to 1; and
weight hourly space velocities (weight of catalyst/weight of
hydrocarbon feedstock/hour) of from about 3 to about 60. These
hydrocarbon cracking conditions are not critical to the present
invention and can be varied depending, for example, on the
feedstock and catalyst being used and the product wanted. The
hydrocarbon cracking reaction is generally conducted in the
essential absence of added free molecular hydrogen.
In addition, the catalytic hydrocarbon cracking system includes an
apparatus for restoring the catalytic activity of catalyst
particles previously used to promote hydrocarbon cracking. This
apparatus involves a catalyst regeneration zone into which at least
a portion of the catalyst from the cracking reaction zone is
withdrawn. Such catalyst is contacted with free oxygen-containing
gas in the regeneration zone to restore or maintain the activity of
the catalyst by removing (e.g., by combusting) carbonaceous
material deposited on the catalyst particles. The combustion gas
temperature in the regeneration zone is generally from about
900.degree. F. to about 1500.degree. F., preferably from about
900.degree. F. to about 1300.degree. F. At least a portion of the
regenerated catalyst is returned or recycled to the hydrocarbon
cracking reaction zone.
The catalyst particles useful in the catalytic hydrocarbon cracking
embodiment of the present invention can be any conventional
catalyst capable of promoting hydrocarbon cracking at the
conditions present in the reaction zone, i.e., hydrocarbon cracking
conditions. Similarly, the catalytic activity of such particles is
restored at the conditions present in the regeneration zone.
Typical among these conventional catalyst are those which comprise
alumina, silica, silica-alumina and at least one crystalline
alumino-silicate having pore diameters of from about 8 .ANG. to
about 15 .ANG. and mixtures thereof. Because of the increased
economic incentive for maintaining the particle size of a
zeolite-containing catalyst, it is preferred that the catalyst
particles comprise from about 1% to about 50%, more preferably from
about 5% to about 25%, by weight of at least one crystalline
alumino-silicate having a pore diameter of from about 8 .ANG. to
about 15 .ANG.. At least a portion of the alumina, silica,
silica-alumina and crystalline alumino-silicate may be replaced by
clays which are conventionally used in hydrocarbon cracking
catalyst compositions. Typical examples of these clays include
halloyside, or dehydrated halloyside (kaolinite), montmorillonite,
bentonite and mixtures thereof. These catalyst compositions can
also contain minor amounts of other inorganic oxides such as
magnesia, zirconia, etc. The compositions may also include minor
amounts of conventional combustion promoters such as the rare earth
metals, in particular, cerium. Such catalyst compositions are
commercially available in the form of relatively small particles,
e.g., having diameters in the range from about 10 microns to about
500 microns, preferably from about 20 microns to about 200
microns.
In general, and except as otherwise provided for herein, the
apparatus of the present invention can be fabricated from any
suitable material or combination of materials of construction. The
material or materials of construction used for each component of
the present apparatus depend upon the particular application
involved. Of course, the apparatus should be made of materials
which are substantially unaffected either physically or chemically,
except for normal wear and tear, by the conditions at which the
apparatus is normally operated. In general, such material or
materials should have no substantial detrimental effect on the
feedstock being chemically converted, the chemical conversion
product or products or the catalyst being employed.
These and other aspects, objects and advantages of the present
invention are set forth in the following detailed description and
claims, particularly when considered in conjunction with the
accompanying drawings in which like parts bear like reference
numerals.
BRIEF DESCRIPTION OF THE DRAWING
In the following detailed description reference will be made to the
following figures:
FIG. 1 is a simplified schematic view of a fluid bed catalytic
hydrocarbon cracking reactor-regeneration system;
FIG. 2 is a horizontal view of a separation device according to the
present invention;
FIG. 3 is a cross-sectional view of the separation device of this
invention, taken along lines 3--3 of FIG. 2;
FIG. 4 shows a side elevation in cross-section of a separation
device which includes a preferred embodiment of an inlet means
according to the present invention;
FIG. 5 is a cross-sectional view taken along line 5--5 of FIG.
4;
FIG. 6 is a cross-sectional view similar to FIG. 5 but showing an
alternative embodiment of the inlet of the present invention;
FIG. 7 is a horizontal view in partial cross-section showing the
lower interior portion of the separation device according to the
present invention and the relationship of a vortex reflector device
thereto; and
FIG. 8 is similar to FIG. 7 but shows an alternative embodiment of
the vortex reflector device of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 there is schematically illustrated a catalytic
hydrocarbon conversion reactor-regenerator system, including a
reactor 10, inlet riser 16, first separator 20, second separator
26, stripper 34, regenerator 48, riser 40, separator 52 and stand
pipe 44. Although the FIGURES and the following description are
directed particularly to a preferred embodiment of the present
invention, catalytic hydrocarbon cracking, the present invention
may be readily adapated to apparatus and methods for other chemical
conversions and catalyst regenerations by those skilled in the
art.
Reactor 10 provides the required space for catalytic hydrocarbon
cracking to occur. Preheated hydrocarbon feedstock, e.g., petroleum
derived gas oil, entering from line 12 is combined with catalyst
particles, e.g., more than 90% by weight of such particles having
diameters greater than about 20 microns, entering from line 14. The
mixture of feedstock and catalyst flows upward through riser 16
where a portion of the catalytic hydrocarbon cracking takes place
and out through a diffuser 17, e.g., a plate with holes positioned
at the top of riser 16, into reactor 10. The feedstock catalyst and
cracked products form a dense fluid bed below level 18. The
particulate matter/vapor mixture in reactor 10 above level 18
comprising cracked products, unreacted feedstock and catalyst
particles is in the form of a lean fluid. This lean fluid enters
first separator 20 tangentially through an inlet 22 to separate a
portion of the solid particles in the lean fluid from the remainder
of the solid catalyst particulate matter/vapor mixture, which is
sent through a line 24 to second separator 26. The separated solid
particles from first separator 20 flow down through a first dip leg
28 to the dense fluid bed below level 18. The solid particulate
matter/vapor mixture in line 24 is conveyed to the top of second
separator 26 which acts to further separate solid particles from
the vapor. Vapor from second separator 26 exits through a line 30
and is sent to product processing, e.g., fractionation or other
chemical reactions and the like, to produce a final saleable
product. The vapor in line 30 may also require additional
processing by using techniques well known to one of ordinary skill
in the art to remove any remaining solid particles. The separated
solid particles leave second separator 26 by second dip leg 32
which exits below level 18 of the dense fluid bed.
Solid particles of catalyst having a carbonaceous deposit thereon
as a result of the conversion reaction are withdrawn from the
bottom of reactor 10 through stripper 34. A stripping gas, e.g.,
steam, enters first stripper 34 through line 35 and acts to strip
hydrocarbon from the solid particles before they exit from reactor
10. The stripped solid catalyst particles exiting from first
stripper 34 flow through a line 36, valve 37, and line 38 where
they are combined with an oxygen-containing gas, e.g., air,
entering via line 39. The resulting mixture of the solid catalyst
particles having a carbonaceous deposit thereon and the
oxygen-containing gas flow through a riser or pipe 40 through a
diffusion plate 41, e.g., a plate with holes, into regenerator 48
containing a fluidized bed of catalyst 42. At least a portion of
the carbonaceous deposit on the solid catalyst particles in
regenerator 48 is removed by combustion with the oxygen-containing
gas. The lean fluid above the catalyst bed 42 in regenerator 48 is
a mixture of solid catalyst particles and vapor. This lean fluid
enters separator 52 via an inlet 66 as shown in greater detail in
FIG. 2 wherein the lean fluid is separated into a vapor stream and
a solid catalyst stream. The vapor exits separator 52 through fluid
outlet 72, and the stream of solid catalyst particles exit
separator 52 through particle outlet 77 for return through third
dip leg 43 to fluid bed 42. The vapor from fluid outlet 72, which
includes combustion flue gases, may be released to the atmosphere
or further processed according to techniques well known to those of
ordinary skill in the art to remove any remaining solid
particles.
Regenerated catalyst solid particles, i.e. catalyst particles which
have had catalytic activity at least partially restored by removal
of carbonaceous deposit, are removed from fluid bed 42 of
regenerator 48 down through a standpipe 44. As the solid catalyst
particles pass through standpipe 44, a fluidizing gas, e.g., steam
entering from line 45, contacts the solid particles, thereby
fluidizing the solid particles in standpipe 44 and stripping any
remaining oxygen-containing gas from the solid particles. The thus
fluidized stripped solid catalyst particles flow from standpipe 44
through line 46, valve 47 and into line 14. The solid catalyst
particles entering from line 14 are combined with the hydrocarbon
feedstock entering the process from line 12 and the cycle is
repeated.
Referring to FIGS. 2 and 3, separator 52 includes a body 53, a
fluid inlet 66, a fluid outlet 72 and a particle outlet 77. Body 53
includes an upright cylindrical wall portion 54, a frusto-conical
bottom portion 55 and a flat top portion 56. Although a cylindrical
body is shown in this preferred embodiment, barrell or other shaped
bodies obvious to one of ordinary skill in the art may also be
used. The upright cylindrical wall portion 54 includes an upper end
57, a lower end 58 and at least one substantially cylindrical
opening 59 near the upper end 57. The opening 59 may have a shape
other than rectangular, such as circular or elliptical, as is known
to one skilled in the art. The frusto-conical portion 55 includes a
wide end 60 and a narrow end 61. The wide end 60 is substantially
the same size as and is attached to the lower end 58 of the
cylindrical wall portion 54. Fluid outlet 72 having a substantially
circular opening 62 passes through flat top portion 56 near its
center. The cylindrical wall portion 54, the frusto-conical bottom
portion 55 and the top portion 56 cooperatively define an enclosed
chamber 63 having a central axis 70, a cylindrical upper portion 64
and a tapered lower portion 65. The cylindrical upper and tapered
lower portions 64, 65 are concentric with the central axis 70.
The fluid inlet 66 includes an inlet conduit 67 having a first end
68, a second end 69 and an open cross-sectional area. The first end
68 of inlet conduit 67 communicates with the particulate
matter/vapor mixture. The second end 69 is connected to the opening
59 near the upper end 57 of the cylindrical wall portion 54,
communicating with the chamber 63 to define an inlet opening 71
having a substantially rectangular cross-sectional inlet area,
"A.sub.i ", which is substantially equal to the cross-sectional
area of the inlet conduit 67. The inlet conduit 67 extends away
from the cylindrical wall portion 54 in a direction substantially
tangential to the cylindrical upper portion 64 of chamber 63 and is
connected to the cylindrical wall portion 54 such that the inlet
opening 71 is positioned at a predetermined inlet radius, "R.sub.i
", which is equal to the distance between the central axis 70 of
said chamber 63 and the centroid of inlet area "A.sub.i ", e.g.,
"R.sub.i " is equal to the average distance between the central
axis 70 and the inlet opening 71.
The fluid outlet 72 includes a substantially cylindrical fluid
outlet conduit 73 having a first end 74, a second end 75 and an
internal radius. The fluid outlet conduit 73 projects through the
substantially circular opening 62 near the center of the top
portion 56 of the body 53 and is attached to the top portion 56
such that the first end 74 of the fluid outlet conduit 73 extends
into the chamber 63 and is concentric with the central axis 70. The
fluid outlet conduit 73 may extend downwardly into the chamber 63
to varying extents. The degree to which the fluid outlet conduit 73
thus extends effects one dimension of the chamber 63 because the
height, "h", of the chamber 63 is defined in relation to the first
end 74 of the fluid outlet conduit 73 in a manner to be explained
later. The fluid outlet conduit 73 at least in part extends axially
away from the chamber 63 in a direction substantially parallel with
the central axis 70 of said chamber 63. The first end 74 of said
fluid outlet conduit 73 communicates with the chamber 63 to define
a fluid outlet opening 76 having an outlet radius, "R.sub.o ",
which is equal to the internal radius of the fluid outlet conduit
73. The outlet area "A.sub.o " of the fluid outlet opening 75 is
simply equal to the cross-sectional area of the fluid outlet
conduit 73, or, in this embodiment .pi.R.sub.o.sup.2.
The particle outlet 77 includes a substantially cylindrical
particle outlet conduit 78 having a first end and a second end. The
particle outlet conduit 78 extends away from the chamber 63 in a
direction substantially parallel and concentric with the central
axis 70 of said chamber 63.
Chamber 63 has a height, "h", equal to the distance between the
first end 74 of the fluid outlet conduit 73 and that point on the
frusto-conical wall 55 which is intersected by an imaginary line
substantially parallel to the central axis 70 and extending from
the first end 74; and a body radius, "R.sub.w ", equal to the
radial distance from the central axis 70 of said chamber 63 to the
interior surface of the cylindrical wall portion 54. If the tapered
lower portion 65 of the chamber 63 is a shape other than tapered or
frusto-conical, e.g., flat, the height "h" would be equal to the
distance of an imaginary line extending from the first end 74 of
the fluid outlet conduit 73 along a line substantially parallel to
the central axis 70 and ending at the point of its intersection
with the bottom portion of the body 53.
The separator or cyclone 52 of this invention is characterized by
dimensions and relationships of certain features which do not exist
in prior art separators or cyclones. In particular, conventional
cyclone theory teaches that cyclone separators should be scaled for
high loading conditions according to either the square root of the
flow rate (in which case particle attrition is held substantially
constant but separation efficiency is lost in larger units) or
according to the cube root of the flow rate (in which case
separation efficiency is held substantially constant, but attrition
is increased in larger units). By way of contrast, this invention
provides a separator which avoids the disadvantageous trade-off of
efficiency versus attrition and in which both high separation
efficiency and low attrition are substantially maintained or
improved in larger units.
The dimensions of the features of the present invention are
determined at least in part by the desired operating conditions.
For example, a cyclone separator intended to process 500 cubic feet
of fluid per second will have different dimensions than a cyclone
separator intended to process 250 cubic feet of fluid per second,
assuming separation efficiency is constant. The present invention
identifies relevant cyclone dimensions and operating parameters and
their numerical interrelationships required for optimum cyclone
operation, i.e. high loading and efficiency with minimization of
particle attrition.
The principal operating parameters upon which the design of the
present separator 52 is based are: (1) tangential wall velocity,
"V.sub.w "; (2) volumetric flow rate, "F"; and (3) critical
particle size, "D". As previously explained, tangential wall
velocity, "V.sub.w ", refers to the linear velocity of particulate
matter within the chamber adjacent the interior surface of the
cylindrical wall portion 56; volumetric flow rate, "F", refers to
the volumetric rate of flow of the inlet stream mixture through
inlet 66, typically expressed in cubic feet per second; and
critical particle size, "D", refers to the diameter of a particle
which has an equal (50%) chance of exiting either by way of
particle outlet 76 or fluid outlet conduit 73.
Also as previously mentioned, it has been found in accordance with
this invention that suitably low attrition is achieved when the
tangential wall velocity, V.sub.w, is maintained at or below about
50 feet per second. For solid particles used to promote hydrocarbon
conversion, the tangential wall velocity "V.sub.w " is preferably
maintained below about 50 feet per second, and generally between
about 40 and about 20 feet per second. In the present invention,
suitably high separation efficiency (on the order of about 95-99%
by weight of solid particles having a diameter greater than about
20 microns) is achieved when the critical particle size is
maintained between about 8 and about 12 microns. In a typical
application such as the reactor 10 shown in FIG. 1, the first stage
separator 20 will operate at a critical particle size of between
about 9 and about 12 microns, and the second stage separator 26
will operate at a critical particle size of between about 8 and
about 10 microns.
The volumetric flow rate, F, is generally fixed, as a practical
matter, at a high volumetric flow rate by predetermined production
factors which cannot readily be controlled. Thus, the separator 52
must be able to provide the desired tangential wall velocity
"V.sub.w " and critical particle size "D" at a given high
volumetric flow rate. The present invention is specifically
directed toward applications where the volumetric flow rate is
between about 200 and about 600 cubic feet per second, preferably
between about 200 and about 350 cubic feet per second.
The dimensions of a separator or cyclone 52 for a desired
application according to the present invention are defined by the
following relationships: ##EQU3## where: K.sub.i =about 3.8
K.sub.a =about 0.016
K.sub.h =about 14
K.sub.o =about 0.017
and where "d" is the density of the particulate matter used to
promote the chemical conversion and "n" is the viscosity of the
particulate matter/vapor mixture.
The relationship between these dimensional features is novel with
respect to separators useful in high loading conditions, e.g., in
excess of about 200 cubic feed per second. Such novel relationships
among the features of the present invention are defined by the
following ratios:
(1) R.sub.i h/R.sub.w.sup.0.89 is less than about 11 ft.sup.1.1 ;
and preferably less than about 9 ft.sup.1.1 ;
(2) R.sub.i A.sub.i is greater than about 16 ft.sup.3 ; and
preferably greater than about 19 ft.sup.3 ; and
(3) hA.sub.i is greater than about 56 ft.sup.3 ; and preferably
greater than about 67 ft.sup.3.
Among the unique dimensions of the present separator 52 is that the
chamber radius, R.sub.w, is larger in relation to other features
than is the case with conventional separators. This aspect gives
separator 52 a "fat" appearance.
In order to understand how the novel features of the invention
effect the operation of the cyclone, it is useful to review the
general operation of cyclones. As previously discussed, the fluid
inlet 16 cooperates with the body 53 and the fluid outlet 72 to
produce vortex flow within the chamber 63. Beginning at the body
wall (R=R.sub.w), the nature of vortex flow within the cyclone is
such that the tangential velocity component "V.sub.t " initially
increases as "R" decreases. At some intermediate point (R=R.sub.m),
the tangential velocity component reaches a maximum (V.sub.t
=V.sub.tm). As "R" further decreases from "R.sub.m " to zero (at
the axis), "V.sub.t " also decreases from its maximum "V.sub.tm "
to zero (at the axis). Thus:
(9) V.sub.t =V.sub.tw when R=R.sub.w ;
(10) V.sub.t .uparw.as R.dwnarw., where R.sub.w
.ltoreq.R.ltoreq.R.sub.m ;
(11) V.sub.t .dwnarw.as R.dwnarw., where R.sub.m
.ltoreq.R.ltoreq.o; and
(12) V.sub.t =O when R=O.
The zone betwen the axis and the intermediate radius "R.sub.m " is
called the core of the vortex. According to the present invention,
achieving low attrition requires providing low tangential wall
velocities, and achieving high separation efficiency requires
providing high tangential velocities, both at the fluid inlet
opening.
Without limiting the scope of this invention to any theory of
operation or use, it is believed that the larger chamber radius
"R.sub.w " or "fat" body results in a slower moving body of air
near the cylindrical wall portion 54. This slower moving body of
air acts as an "air cushion", reducing the effective tangential
velocity of the particulate matter near the wall, "V.sub.w ", and
thus minimizing attrition by minimizing the collisions between the
solid particles and the wall. In contrast to conventional cyclones,
wherein an increased chamber radius "R.sub.w " results in decreased
overall separation efficiency, defining the other critical features
according to this invention results in a cooperation with the
"R.sub.w " factor that maintains or increases separation
efficiency.
EXAMPLE
The design of a cyclone separator according to the present
invention can be illustrated and compared with prior art designs by
the following example, which assumes a high volumetric flow rate,
"F", of 316.7 ft.sup.3 per second, a desired tangential wall
velocity, "V.sub.w ", of about 40 ft/sec and a critical particle
diameter, D, of 10.9 microns. It should be noted that a tangential
wall velocity of about 40 ft/sec and a critical particle diameter
of 10.9 microns has been found to provide very acceptable levels of
low attrition and high separation efficiency in a first stage
separation of conventional catalyst particles used to promote
hydrocarbon conversion.
The following Table I compares the dimensional and operational
characteristics of a separator according to the present invention
with a separator of conventional design. The conventional cyclone
was manufactured by the Buell Engineering Co. of Lebanon, Pa. Model
No. 64AC-350B.
TABLE I ______________________________________ Inventive
Conventional Design Design ______________________________________
Dimensional Feature Inlet gas stream viscosity, 0.0004 0.0004 poise
(n) Particulate matter density 1.4 1.4 g/cc (d) Inlet radius, ft
(R.sub.i) 3.23 3.3 Body radius, ft (R.sub.w) 4.46 2.75 Outlet
radius, ft (R.sub.o) 0.95 0.94 Internal height, ft (h) 11.56 11.8
Inlet area, ft.sup.2 (A.sub.i) 6.12 6 Operating Characteristic
Vapor flow rate, ft.sup.3 /sec (F) 316.7 316.7 Tangential wall
velocity, 40.0 58.9 ft/sec (V.sub.w) Critical particle diameter,
10.9 10.9 microns (D) Fraction of catalyst converted 3.15 .times.
10.sup.-6 11.4 .times. 10.sup.-6 to sub-20-micron sized fines
(E.sub.u) ______________________________________
The fraction of catalyst which is converted to sub20 micron sized
fines indicates the cyclone's conventionally defined attrition
rate, i.e., the fraction of a typical equilibrium catalyst which
would be comminuted to less than 20 micron size by collision with
the body wall at the operative tangential wall velocity. In the
present example, the cyclone of the present invention reduces
attrition rate over that of the conventional design judged
according to conventional definition by a factor of about 3.6. Even
larger reductions in the attrition rate are possible when comparing
the cyclone of the present invention to conventional cyclones
having initially higher tangential wall velocities.
The following Table II provides a comparison of the dimensional
ratios (e.g. as defined by Relationships (1)-(3)) of the separators
described in Table I.
TABLE II ______________________________________ Invention
Conventional Ratio Design Design
______________________________________ R.sub.i h/R.sub.w.sup..89
9.9 ft.sup.1.1 15.8 ft.sup.1.1 R.sub.i A.sub.i 19.8 ft.sup.3 19.8
ft.sup.3 hA.sub.i 70.7 ft.sup.3 70.8 ft.sup.3
______________________________________
The difference in dimensions and dimensional ratios shown in Tables
I and II are believed to be typical and representative of the
differences between a cyclone separator according to the present
invention and according to the prior art for a given high loading
application.
Separator 52 of the the present invention can utilize a variety of
inlet designs known to those skilled in the art, e.g. a single
tangential inlet 66 as shown in FIGS. 2 and 3, or an axial inlet
where the fluid mixture is introduced in a generally downward
direction. A particularly preferred inlet 82 is shown, however, in
FIGS. 4 and 5 which further minimizes particle attrition while
introducing the fluid mixture at a high inlet velocity into a
separator, e.g., between about 40 and about 75 feet per second. The
separator 80 is substantially similar to separator 52 except for
inlet 82. As a result, the items in separator 80, as shown in FIGS.
4 and 5, will be identified in the same manner as the items in
separator 52 of FIGS. 2 and 3, except for the inlet 82. Referring
to FIGS. 4 and 5, the inlet 82 includes a top annular plate 86, a
bottom annular plate 87, a plurality of substantially vertical
plates on inlet vanes, as identified hereinafter, and an upright
cylindrical wall portion 54 of body 53.
The upright cylindrical wall portion 54 of separator 80 as
illustrated in FIG. 5 has a cylindrical circumference and an
opening around the circumference near the upper end 57 thereby
defining a substantially cylindrical opening 83 to the chamber 63
within the cylindrical wall portion 54. The cylindrical opening 83
has a top edge 84 and a bottom edge 85.
Top and bottom solid annular plates 86 and 87 have inner edges 88,
89, respectively, an inner radius, "R.sub.I ", outer edges 90, 91,
respectively, and an outer radius which is substantially equal to
said chamber radius, "R.sub.w ". The top and the bottom annular
plates 86, 87 are each preferably positioned within the upper
cylindrical portion 64 of the chamber 63 parallel to the flat top
portion 56 of the body 53. More specifically, the outer edge 90 of
the upper plate 86 is preferably adjacent to the top edge 84 of the
cylindrical opening 83 and forms a first interface therewith, and
the outer edge 91 of the lower plate 87 is adjacent to the bottom
edge 85 of the cylindrical opening 83 to form a second interface
therewith. The upper and lower plates 86, 87 are attached to the
cylindrical wall portion 54 such that a seal is formed along the
first and second interfaces. The upper and lower annular plates 86,
87 define an annular or doughnut shaped space within the chamber 63
which is in communication with the cylindrical opening 83 in the
cylindrical wall portion 54. The annular shaped space in chamber 63
further communicates through a conventionally designed collar and
inlet conduit (not shown) to a fluid intake, such as the conduit
inlet 22 shown in FIG. 1, which supplies the particulate matter
vapor mixture.
The operation of inlet 82 will be explained by specific reference
to the three inlet plates or vanes 92, 84, and 96, as shown in FIG.
5. It is to be understood, however, that all of the inlet vanes are
preferably substantially similar in design, and they function in a
substantially similar manner.
The plurality of substantially rectangular plates or inlet vanes
92, 94 and 96 have a predetermined axial width, "w", axial length,
"1", and axial thickness, "k", and are positioned symmetrically
within the annular shaped space about the central axis 70 of said
chamber 63 such that the axial width "w" extends between the upper
and lower annular plates, 86, 87; the axial length "1" extends
between the inner edges 88, 89 and the outer edges 90, 91 of the
annular plates 86, 87 in a direction which is substantially
perpendicular to the inner radius, "R.sub.I, of the annular plates
86, 87 and the axial thickness is substantially parallel to the
inner radius "R.sub.I " on the inner edges 88, 89 of the upper and
lower annular plates 86, 87.
The plurality of rectangular plates 92, 94 and 96 are preferably
positioned in a substantially symmetrical and circular
configuration about the chamber and divide the annular space into a
plurality of passageways 98, 100, 102 which are, therefore, also
preferably symmetrically positioned about the central axis 70. The
circular configuration has a radius which is preferably at least
twice the fluid outlet radius "R.sub.o ". The plurality of
passageways 98, 100, 102, have a narrow arcuate inner end (e.g.,
see inner end 103 of passageway 98) in communication with the
chamber 63 and a wide arcuate outer end (e.g., see outer end 104 of
passageway 98) in communication with the collar and conduit (not
shown) and the first fluid stream mixture. The inner end 103
defines an inlet opening positioned at a distance from the central
axis 70 of the chamber 63 equal to "R.sub.I ". It should be noted
that "R.sub.i " of Relationships (1)-(8) equals "R.sub.I
"+".sub.2.sup.W ", where "W" is discussed hereinafter.
The distance separating any two adjacent vanes is preferably given
by the relationship:
where "N" equals the number of inlet vanes. The total inlet area
A.sub.I is therefore:
A.sub.I =NWR.sub.I [1-cos (360/N)].
("A.sub.I " equals "A.sub.i " of Relationships (1)-(8).)
The plurality of passageways 98, 100, 102 divide the first fluid
stream mixture into a plurality of high velocity inlet streams
(indicated in FIG. 5 by arrows 105, 106, 107) and introduce the
inlet streams 105, 106, 107 into the chamber 63 at a plurality of
locations symmetrically positioned about the central axis 70 of the
chamber 63 at a distance, "R.sub.I," from the central axis 70. The
passageways 98, 100, 102 can comprise any suitable structure which
provides means for introducing a fluid stream into a chamber, for
example, channels or conduits. More preferably, as shown herein,
the vertical wall portions of such passageways comprise vanes, and
the top and bottom portions can comprise any suitable enclosing
structures, for example, arcuate or flat surfaces. Each inlet
stream 105, 106, 107 is introduced in a direction which is
substantially perpendicular to the chamber radius "R.sub.w " and
substantially tangential to the chamber 63. Each inlet stream
deflects another inlet stream from the body and the inlet vanes and
is, in turn, away itself deflected away from the body and the inlet
vanes by another inlet stream. For example, inlet stream 106
intersects and deflects inlet stream 105 just prior to the location
at which inlet stream 105 would otherwise impinge inlet valve 94,
and inlet stream 106 is intersected and deflected by inlet stream
107 just prior to the location at which inlet stream 106 would
otherwise impinge inlet vane 96. The inlet streams 105, 106, 107,
cooperate in this manner to introduce the first fluid stream
mixture into the chamber 63 at a high rate of velocity, increasing
the centrifugal forces and separation efficiency, while
simultaneously reducing collision between the solid particles of
the mixture and any surfaces of the cyclone apparatus, thereby
minimizing attrition attributable to the fluid inlet 82.
Another advantage of the design of fluid inlet 82 is that it
facilitates centering of the vortex within the chamber 63. That is,
since the particulate matter/vapor mixture is introduced as a
plurality of inlet streams located symmetrically about the center
axis 70 and since the plurality of inlet streams co-act by
deflection of one another to produce a generally circular flow
pattern, which is itself centered about axis 70, the resulting
vortex tends also to be well centered within the chamber 63.
Alternatively, offsetting the vortex with respect to the center
axis 70, if desired, could be facilitated by positioning all of the
inlet vanes such that the inlet openings are offset a predetermined
distance with respect to the center axis 70.
The angle of deflection of the inlet streams 105, 106, 107 is an
important factor in the efficiency of the inlet 82 in minimizing
attrition. Generally, the smaller the angle of deflection, the more
effective are the inlet streams 105, 106, 107 in deflecting one
another and preventing impingment and attrition. As a result, inlet
82 also avoids turbulence, which is a disruptive factor to vortex
formation. In other words, the more incremental the deflection, the
more efficient the inlet 82.
The angle of deflection 82 can be adjusted in several ways. For
example, the number of primary inlet vanes 92, 94, 96 positioned
symmetrically about the axis 70 can be increased, which will reduce
the angle of deflection. Similarly, the primary inlet vanes 92, 94,
96 can be repositioned directly such that they are angled more
inwardly or outwardly (compare, for example, inlet vanes 108 and
108' in FIG. 5). It should be noted however, that the latter
technique will also change the inlet radius "R.sub.I " and the
inlet area "A.sub.I " which will directly effect operation of the
cyclone of this invention. Since the inlet radius "R.sub.I " and
inlet "A.sub.I " in connection with this invention are calculated
in relation to the desired operating parameters and the inlet 82
must be designed accordingly, the preferred technique for adjusting
the angle of deflection in accordance with this invention is to
increase or decrease the number of inlet vanes.
The inlet radius "R.sub.I " and the inlet area "A.sub.I " may be
adjusted, as desired, by several different techniques. One such
technique, as described above, is to reposition the inlet vanes
105, 106, 107 such that they are angled more inwardly or outwardly.
Alternatively, the axial length, "1", of the inlet vanes 105, 106,
107 can be shortened, or the inlet vanes can be repositioned to
extend outside of the upright cylindrical wall portion 54.
(Compare, for example, inlet vanes 109 and 109' shown in FIG. 5.)
The inlet 82 could be designed, for example, with the vanes 92, 94,
96 being positioned entirely outside of the chamber 63, such that
the narrow end 103 of passageway 98 communicates with the chamber
63 at the cylindrical opening 83 in upright cylindrical wall
portion 54, (e.g., "R.sub.I " would equal "R.sub.w ".)
The top and bottom annular plates 86, 87 can alternatively be made
frusto-conical in contrast to the substantially flat design shown
in FIG. 4. In this way the inlet streams 105, 106, 107 have a
downward directional component as well as tangential component,
facilitating vortex formation.
Referring to FIG. 6, the inlet 82 is shown in an alternative
embodiment which includes a plurality of secondary vanes, each
secondary vane being substantially parallel to and associated with
one primary inlet vane. Except for the secondary vanes and the
inlet passages, the inlet shown in FIG. 6 is substantially
identical to the inlet 82 shown in FIG. 5. The present embodiment
will be explained by reference to secondary inlet vanes 110, 111,
and 112 which are associated with primary inlet vanes 92, 94 and 96
respectively. It is to be understood, however, that the remaining
secondary vanes are designed and function in a substantially
similar manner.
The secondary vanes 110, 111, and 112 are preferably substantially
parallel to and cooperate with the primary inlet vanes 92, 94, and
96, respectively, to define guides or inlet passages 113, 114, 115
of substantially uniform size along a predetermined length and a
non-functional area therebetween (indicated by shading in FIG. 6).
The guides or inlet passages 113, 114, 115 define means for
accelerating the inlet stream associated with the inlet vane to a
predetermined inlet velocity before introducing the inlet stream
into the chamber. This design is, in effect, similar to placing a
plurality of inlets such as inlet 66 shown in FIG. 3 symmetrically
about the chamber 63. Alternatively, the secondary vanes 110, 111,
112 may be placed transverse to the inlet vanes 92, 94, 96, to form
a converging inlet which continually increases the velocity of the
inlet stream similar to the passageways 98, 100, 102 shown in FIG.
5. The parallel placement of the secondary vanes is preferred in
this embodiment because it provides inlet streams 116, 117, 118
which achieve a constant desired velocity prior to entering the
chamber 63. Constant velocity allows the inlet streams 116, 117,
118 and entrained gas particles to achieve a smooth, non-turbulant
flow pattern and to enter the cyclone with as little disruption as
possible of the existing flow pattern within the chamber 63. Since
the inlet streams 116, 117, 118 achieve a smooth, non-turbulent
flow, they are believed highly effective in deflecting the adjacent
inlet streams and reducing attrition attributable to the inlet
82.
Referring now to FIG. 7, another aspect of a separation device of
the present invention comprises a vortex reflecting device 120
which includes a plate 121, a support rod 122, and a reflecting
disk 123.
Plate 121 having a plurality of holes 124 near its outer edge is
positioned horizontally within the lower tapered portion 65 of the
chamber 63 and is attached to the frusto-conical wall portion 55
along the outer edge of the plate 121, thereby effectively dividing
the chamber 63 into a separation zone 125 and a collection zone
126. The separation zone 125 (e.g., in which the vortex is located)
communicates with the fluid inlet 66 and the fluid outlet 72 in
substantially the same manner as previously explained for FIGS.
1-5. Those aspects of the device which have been explained
elsewhere will be referred to by their previous numbers, although
they will not be repeated in FIG. 6 for purposes of simplicity. The
collection zone 126, in turn, communicates with the particle outlet
77. The plate 121 is preferably substantially solid, except for
holes 124, to prevent the vortex from entering the collection zone
126. Moreover, the plate 121 is preferably circular in shape to
best fit into the tapered lower portion 65 of the chamber 63. Other
shapes, e.g. hexagonal or frusto-conical, known to one skilled in
the art may also be used. The holes 124 in the plate 121 define
passageways from the separation zone 125 to the collection zone
126, thereby allowing the solid particles that have collected along
the interior surface of the cylindrical and frusto-conical wall
portions 54, 55 to drift downward and to pass from the separation
zone 125 into the collection zone 126, and, ultimately, out of the
particle outlet 77.
Although the holes 124 may be located slightly inward from the edge
of the plate 121, they are preferably located as near the edge as
possible. The particularly preferred location for holes 124 are
notches around the edge. In this way, the solid particles can drift
downward while near the wall. As a result, they do not have to
migrate toward the central axis 70 where they might be entrained by
the vortex and carried out the particle outlet 77.
The support rod 122, having a first end 127 and a second end 128 is
located within the separation zone 125. The first end 127 of the
support rod 122 is attached to the center of the substantially
solid circular plate 121. The rod 122 extends from the plate 121
toward the fluid outlet opening 72 in a direction substantially
parallel to said central axis 70 of said chamber 63.
The reflecting disk 123 has a first side and a second side and is
mounted upon the support rod 122 such that the second end 128 of
the support rod 122 is secured to the center of the first side of
the reflecting disk 123. In this way, the reflecting disk 123 is
centrally mounted within the chamber 63 and, preferably, is
centrally located with respect to the vortex. This arrangement is
preferred as the most effective design to reflect the vortex. The
reflecting disk 123 is preferably solid, circular and flat for the
same reasons as explained in connection with the plate 121. The
reflecting disk 123 has a disk radius which is at least as large as
the fluid outlet radius, preferably twice as large, so that the
reflecting disk 123 effectively prevents the vortex from extending
below the disk. When the reflecting disk 123 is so designed as to
prevent the vortex from extending below the disk, the reflecting
disk functions as the bottom floor of the separator, i.e., for
purposes of defining "h" as shown in FIG. 2, the height "h" would
be equal to the average distance from the fluid outlet 76 to the
reflecting disk 123.
The centering plate 121, support rod 122 and the reflecting disk
123 cooperate to define the vortex reflecting device 120 which
prevents re-entrainment of particulate matter that has once been
effectively separated from the vapor. Without the vortex reflecting
device 120, particulate matter which has drifted downward into the
tapered lower portion 65 of the chamber 63 has a tendency to be
picked up by the vortex and re-entrained in the fluid outlet
stream. Even if the circular plate 121 is utilized without the
reflecting disk 123 particulate matter tends to drift inward along
the plate 121 toward the vortex, ultimately to be carried out the
fluid outlet 72. The reflecting disk 123 used in conjunction with
the primary plate 121 defines a dead zone therebetween. The vortex
does not enter this dead zone, and there is no vapor flow in the
dead zone sufficient to cause re-trainment of the particulate
matter. More efficient vortex reflection and particle separation
results.
The reflecting disk 123 may be mounted on the plate 121 by
arrangement other than a single supporting rod 122. For example, a
plurality of braces 130 provide an alternative tripod support
structure (shown in FIG. 6 by dotted lines). Alternately, the
supporting rod 122 could comprise a spring mechanism (not shown).
This latter arrangement would have the advantage of permitting the
reflecting disk 123 to move along with the vortex in response to
dynamic conditions within the chamber. For example, if the vortex
shifted temporarily to one side, or increased in intensity, the
spring mechanism 122 would allow the reflecting disk to shift from
side to side or to move toward or away from the fluid outlet to
counteract the changing conditions. Importantly, however, the
reflecting disk 123 as mounted above the primary plate 121 should
not be mounted in a manner that would interfere with the vortex or
the flow patterns within the separation zone 125. For example,
interference would result if the reflecting disk 123 were supported
from the top wall portion 56 by rods which extend through the core
of the vortex. Thus the preferred arrangement is to support the
reflecting disk 123 from its underside.
The vortex reflector 126 may further include a vortex centering
device for adjusting the position of a vortex within the chamber.
The vortex centering device comprises an elongated centering member
131 such as cylindrical or cigar-shaped projection having a first
end and a second end. The first end of the elongated member or
centering rod 131 is attached to the second side of the reflecting
disk 123 at the center thereof and extends upward therefrom toward
the fluid outlet 72 into the center of the vortex. The centering
rod 132 helps to center and to adjust the position of the vortex
within the separation zone 120 of the chamber 63. As a result, the
flow of the vortex about the centering rod 131 creates resistance
forces which are at a minimum when the rod 131 is centered in
relation to the vortex. If the vortex moves such that the centering
rod 131 becomes off center with respect to the vortex, the
resistance forces increase. The vortex will tend to remain centered
with respect to the centering rod so as to minimize these
resistance forces. In particular, locating the centering rod 131 in
the center of the reflecting disk helps to maintain the vortex in a
position directly over the reflecting disk 123, thereby
facilitating formation of the dead zone between primary plate 121
and reflecting disk 123.
The plate 121, which was shown as a substantially flat disk in FIG.
7, may alternatively comprise a conical shaped primary plate 134 as
shown in FIG. 8. The conical shaped primary plate 134 is
substantially similar to the primary plate 121 of FIG. 7 except for
the conical shape. The conical shape provides "gravity-assist"
forces to direct separated particulate matter through the openings
135 near the edge of the plate 134, into the collection zone 126
and out of particle outlet 77. Also as shown in FIG. 8, the
reflecting disk 138 may be of conical, hemispherical or other
shapes known to one skilled in the art.
It is to be understood that the foregoing description relates to
specific embodiments and that alternative embodiments and
modifications of the present device are possible without departing
from the intended scope of the invention.
* * * * *